Tin and tin/lead alloy deposits are useful for the electronics industry, particularly in the manufacture of printed circuit boards, electrical contacts and connectors, semi-conductors, electrical conduit, and other related parts where the inherent properties of these deposits are necessary. In recent years, tin and tin/lead alloys have been rapidly deposited in high speed plating machines equipped with jet agitation or vigorous solution movement. High speed plating is achieved through the use of high current densities at high cathode efficiencies, which can often be obtained through the use of vigorous agitation and elevated solution temperatures. All plating electrolytes for plating tin and tin/lead alloy deposits can achieve some degree of high speed plating provided that there is an increase in agitation, total concentration of the electrolyte, and/or solution temperature.
Modern tin and tin/lead alloy plating baths require tin to exist in the divalent state. A number of factors present during the electroplating process can cause the oxidation of tin from the divalent state to the tetravalent state. In high speed electroplating process, for example, the rapid pumping action and solution movement common to high-speed plating machines causes air to be mixed with the solution, thereby promoting such oxidation. This oxidation is accelerated due to the elevated temperature of operation which is commonly used in high-speed plating installations.
When divalent tin becomes tetravalent, it tends to precipitate in the bath as stannic oxide, thereby forming a tin-sludge with a corresponding loss of available tin for electrodeposition. The sludge reduces the efficiency of the bath and causes operating problems because of its tendency to clog the jets and spargers of the agitation system. This, in turn, results in frequent and costly production shutdowns for cleanup and removal. It is therefore very important to use plating baths which will substantially limit the formation of tetravalent tin under the particular electroplating conditions used.
Pyrocatechol, resorcinol, hydroquinone and similar compounds have been used as anti-oxidants in fluoboric acid/tin plating solutions. The high-speed plating of tin and tin alloys obtained from solutions that have been formulated with metal fluoborates and free fluoboric acid. In spite of the fact that the known anti-oxidants are incorporated into these fluoboric acid formulations, experience in high-speed plating applications has shown that large quantities of tin sludge are nevertheless formed during electrolysis.